Group living
Many animal species live in groups. Biologists used to think that group-living animals exhibit self-sacrificing behaviors that benefit the group. Some animals limit their rate of eating even when they still need food. Less cooperative groups may exhaust their food supply and therefore perish. Today, however, it is generally agreed that except for a few unusual circumstances, individuals in a group behave in ways that benefit themselves. Group living occurs when the gains it brings to an individual outweigh the costs.
One benefit an individual animal can get from living in a group is increased vigilance. A leopard depends on the element of surprise to catch an antelope. If the antelope spots the leopard quickly enough, it can run away. A single antelope doesn’t have an infinite supply of vigilance, however; for one thing, it has to spend much of its time with its head to the ground to graze(eat). But if individual antelopes come together in a group, they in effect acquire more eyes and ears. In addition to being less likely to be surprised, the antelopes can also spend more time eating-which can raise their individual fitness even more relative to solitary antelopes. And even if a predator does strike a group of antelopes, each group member faces a smaller risk (a phenomenon known as the dilution effect). Animal groups produced by dilution effects are often called selfish herds, because their herding behavior is not based on any coordination or cooperation but is instead the result of a selfish scramble of individuals competing for a position near the center of the group.
Adelie penguins, which live on the coast of Antarctica, vividly illustrate how group living allows individuals to escape predators. They dive off ice sheets into the ocean to search for fish; but when they take the plunge, they sometimes get eaten by leopard seals cruising just offshore. Rather than jump in alone, the penguins crowd together by the hundreds and then leap as a group. Together, they can overwhelm the leopard seals, which can’t focus on any single individual. The huge numbers of jumping penguins may also create a dilution effect because the likelihood of any individual being caught is reduced. Predators can benefit from group living as much as prey. American white pelicans practice “fish herding,”paddling on the water together in a tactical formation to drive fish into shallows or into dense concentrations; the birds can then easily scoop up their prey. Each pelican in a fish-herding team gets more prey than if it foraged alone.
While living in groups can bring many benefits, it can impose costs as well. Individuals living in big groups are at greater risk of getting sick, for instance. Parasites and diseases can spread more effectively in dense groups of animals than among solitary animals. Large groups also present more opportunities to mate. Females may benefit from these opportunities because they can mate with higher-quality males. Males that can mate with many females can also enjoy higher reproductive success. In species where males provide parental care, group living may also mean that many males are not actually the fathers of the offspring they are caring for. Finally, living in a group often means more competition for limited food, space, or other resources.
By measuring the costs and benefits of group living in particular cases, biologists can explain why individual members of social groups behave in the ways they do. One of the most important lessons from such studies is that the costs and benefits of a given action will be different for different individuals. A large, dominant animal may be able to reap the greatest benefits of residing in a group-for example, being in the safest, central part of the group- and at the same time pay only minimal costs. Dominant individuals are likely to prevail in any competition for food or other resources, so that they suffer little loss from being in the group. Costs are higher for subordinate individuals-a young meerkat in a group, for example, has to help rear the offspring of the dominant meerkats, but since it faces a high risk of being killed by a predator if it lives on its own, this may still be a small price to pay.
1
Many animal species live in groups. Biologists used to think that group-living animals exhibit self-sacrificing behaviors that benefit the group. Some animals limit their rate of eating even when they still need food. Less cooperative groups may exhaust their food supply and therefore perish. Today, however, it is generally agreed that except for a few unusual circumstances, individuals in a group behave in ways that benefit themselves. Group living occurs when the gains it brings to an individual outweigh the costs.
Why does the author make the point that “Some animals limit their rate of eating even when they still need food”?
ATo provide an argument in favor of an early view of group living
BTo show what happens after groups of animals exhaust their food supply
CTo provide an example of animal behavior that is not as cooperative as it may look
DTo support the idea that it is unusual for individual animals to behave in ways that benefit the group
2
Many animal species live in groups. Biologists used to think that group-living animals exhibit self-sacrificing behaviors that benefit the group. Some animals limit their rate of eating even when they still need food. Less cooperative groups may exhaust their food supply and therefore perish. Today, however, it is generally agreed that except for a few unusual circumstances, individuals in a group behave in ways that benefit themselves. Group living occurs when the gains it brings to an individual outweigh the costs.
According to paragraph 1， self-sacrificing behaviors within animal groups are now believed to
Abe the basis of group living
Brequire cooperation from the other individuals in the group
Coccur only rarely
Dhave unexpected benefits
3
One benefit an individual animal can get from living in a group is increased vigilance. A leopard depends on the element of surprise to catch an antelope. If the antelope spots the leopard quickly enough, it can run away. A single antelope doesn’t have an infinite supply of vigilance, however; for one thing, it has to spend much of its time with its head to the ground to graze(eat). But if individual antelopes come together in a group, they in effect acquire more eyes and ears. In addition to being less likely to be surprised, the antelopes can also spend more time eating-which can raise their individual fitness even more relative to solitary antelopes. And even if a predator does strike a group of antelopes, each group member faces a smaller risk (a phenomenon known as the dilution effect). Animal groups produced by dilution effects are often called selfish herds, because their herding behavior is not based on any coordination or cooperation but is instead the result of a selfish scramble of individuals competing for a position near the center of the group.
The word “infinite”in the passage is closest in meaning to
Asignificant
Bsufficient
Creliable
Dendless
4
One benefit an individual animal can get from living in a group is increased vigilance. A leopard depends on the element of surprise to catch an antelope. If the antelope spots the leopard quickly enough, it can run away. A single antelope doesn’t have an infinite supply of vigilance, however; for one thing, it has to spend much of its time with its head to the ground to graze(eat). But if individual antelopes come together in a group, they in effect acquire more eyes and ears. In addition to being less likely to be surprised, the antelopes can also spend more time eating-which can raise their individual fitness even more relative to solitary antelopes. And even if a predator does strike a group of antelopes, each group member faces a smaller risk (a phenomenon known as the dilution effect). Animal groups produced by dilution effects are often called selfish herds, because their herding behavior is not based on any coordination or cooperation but is instead the result of a selfish scramble of individuals competing for a position near the center of the group.
Which of the sentences below best expresses the essential information in the highlighted sentence in the passage? Incorrect choices change the meaning in important ways or leave out essential information.
AAnimal groups produced by dilution effects often include some selfish individuals that scramble for a position near the center instead of participating in herding behavior.
BDilution effects are generally caused by individuals who get a position near the center of the group, not by coordination or cooperation within the animal group.
CThe behavior of animal groups that are produced by dilution effects is not a result of coordination or cooperation but of selfish competition for a position near the center.
DAnimal groups may coordinate and cooperate to achieve dilution effects but are still called selfish herds because their members compete for positions at their centers.
5
One benefit an individual animal can get from living in a group is increased vigilance. A leopard depends on the element of surprise to catch an antelope. If the antelope spots the leopard quickly enough, it can run away. A single antelope doesn’t have an infinite supply of vigilance, however; for one thing, it has to spend much of its time with its head to the ground to graze(eat). But if individual antelopes come together in a group, they in effect acquire more eyes and ears. In addition to being less likely to be surprised, the antelopes can also spend more time eating-which can raise their individual fitness even more relative to solitary antelopes. And even if a predator does strike a group of antelopes, each group member faces a smaller risk (a phenomenon known as the dilution effect). Animal groups produced by dilution effects are often called selfish herds, because their herding behavior is not based on any coordination or cooperation but is instead the result of a selfish scramble of individuals competing for a position near the center of the group.
According to paragraph 2， antelopes benefit from group living in all of the following ways EXCEPT:
ALeopards and some other predators avoid attacking large groups of antelopes.
BThe antelopes are more likely to react to the predator early enough to escape.
CThe antelopes can increase their fitness by eating for longer periods of time
DThe antelopes benefit from the dilution effect.
6
Adelie penguins, which live on the coast of Antarctica, vividly illustrate how group living allows individuals to escape predators. They dive off ice sheets into the ocean to search for fish; but when they take the plunge, they sometimes get eaten by leopard seals cruising just offshore. Rather than jump in alone, the penguins crowd together by the hundreds and then leap as a group. Together, they can overwhelm the leopard seals, which can’t focus on any single individual. The huge numbers of jumping penguins may also create a dilution effect because the likelihood of any individual being caught is reduced. Predators can benefit from group living as much as prey. American white pelicans practice “fish herding,”paddling on the water together in a tactical formation to drive fish into shallows or into dense concentrations; the birds can then easily scoop up their prey. Each pelican in a fish-herding team gets more prey than if it foraged alone.
The word “formation” in the passage is closest in meaning to
Amovement
Bdecision
Cattack
Darrangement
7
Adelie penguins, which live on the coast of Antarctica, vividly illustrate how group living allows individuals to escape predators. They dive off ice sheets into the ocean to search for fish; but when they take the plunge, they sometimes get eaten by leopard seals cruising just offshore. Rather than jump in alone, the penguins crowd together by the hundreds and then leap as a group. Together, they can overwhelm the leopard seals, which can’t focus on any single individual. The huge numbers of jumping penguins may also create a dilution effect because the likelihood of any individual being caught is reduced. Predators can benefit from group living as much as prey. American white pelicans practice “fish herding,”paddling on the water together in a tactical formation to drive fish into shallows or into dense concentrations; the birds can then easily scoop up their prey. Each pelican in a fish-herding team gets more prey than if it foraged alone.
According to paragraph 3， in which TWO of the following ways does diving off ice sheets together benefit Adelie penguins? To receive credit, you must select TWO answers.
AIt can distract predators from making an effective attack.
BIt overwhelms the penguins’ prey fish, making the fish easier to catch.
CIt makes it less likely for each penguin to get caught if a predator attacks successfully.
DIt allows the penguins to drive leopard seals away from the offshore area.
8
By measuring the costs and benefits of group living in particular cases, biologists can explain why individual members of social groups behave in the ways they do. One of the most important lessons from such studies is that the costs and benefits of a given action will be different for different individuals. A large, dominant animal may be able to reap the greatest benefits of residing in a group-for example, being in the safest, central part of the group- and at the same time pay only minimal costs. Dominant individuals are likely to prevail in any competition for food or other resources, so that they suffer little loss from being in the group. Costs are higher for subordinate individuals-a young meerkat in a group, for example, has to help rear the offspring of the dominant meerkats, but since it faces a high risk of being killed by a predator if it lives on its own, this may still be a small price to pay.
Paragraph 5 suggests that young meerkats provide care to offspring of other meerkats because doing so
Aenables the young meerkats to stay in the group and thus increases their chances of survival
Bmakes the young meerkats more likely to become dominant when older
Cgives the young meerkats access to the central part of the group
Dallows the young meerkats to access more food and other resources
9
While living in groups can bring many benefits, it can impose costs as well. Individuals living in big groups are at greater risk of getting sick, for instance. Parasites and diseases can spread more effectively in dense groups of animals than among solitary animals. [■]Large groups also present more opportunities to mate. Females may benefit from these opportunities because they can mate with higher-quality males. [■]Males that can mate with many females can also enjoy higher reproductive success. [■]In species where males provide parental care, group living may also mean that many males are not actually the fathers of the offspring they are caring for. Finally, living in a group often means more competition for limited food, space, or other resources.[■]
Look at the four squaresthat indicate where the following sentence could be added to the passage
But while this is a benefit for some individuals in the group, it is a cost for others.
Where would the sentence best fit？Click on a square sentence to the passage.
10
Biologists have studied animals that live in groups.
AThe benefits of being in a group include a lower chance of getting eaten for group-living prey animals and a greater ability to obtain food for group-living predators.
BWhen a group of animals exhausts most of its food supply or other resources, cooperation among the individuals in the group decreases.
CThe largest members benefit the group by defending weaker members from predators and making the group more likely to prevail in competitions against other groups.
DWhile group living often imposes costs, they are usually lower for each group-living animal than the benefits it gets from being in the group.
EDominant individuals are able to obtain the most benefits from being in a group, while subordinate ones have the most costs.
FBiologists now recognize that animals in groups exhibit both self- sacrificing and selfish behaviors, which differ greatly among the individuals in the group.
